Only an external impact could have caused a Russian plane to dive into the Egyptian desert, killing all 224 people on board, Metrojet airline officials have said.

The firm's claim added to a series of confusing statements from investigators that left an unclear picture over what caused the plane to break up mid-flight.

"We rule out a technical fault of the plane or a pilot error," Metrojet deputy general director Alexander Smirnov said. "The only possible explanation could be an external impact on the plane."

When pressed for more details about the type of impact and what could have caused it, Mr Smirnov said he was not at liberty to discuss details because the investigation was ongoing.

Russian aviation authorities called the company comments premature, but Mr Smirnov defended his position.

He said the plane dropped 186mph in speed and about 5,000ft in altitude one minute before it crashed on Saturday.

Mr Smirnov described the A321-200 as a reliable aircraft that would not fall into a spin even if the pilots made a grave error because its automatic systems would correct crew mistakes.

The Airbus plane was flying at 31,000ft when it crashed soon after taking off from Sharm el-Sheikh en route to St Petersburg.

Prime Minister David Cameron said people should not stop flying to the popular Red Sea resort because of the company's claims.

He added: "If anything changes, we don't sit around and chew our pens and not act. If anything changes, it will be announced very quickly. But, as I say, we must do it on the basis of evidence and not on speculation."

Military analyst Paul Beaver said that he thought the crash was most likely caused by a bomb on board. He added that he was certain Islamic State - who initially claimed responsibility for the crash - did not possess a missile system capable of hitting the plane.

"I'm pretty convinced that they don't have a double-digit surface-to-air missile," he said. "That is [what is] necessary to go up as far as 31,000 feet. That's a very serious piece of equipment, and I don't think they have that sophistication."